Relationship Between Content of Ketone Bodies in Milk and Milk Freezing Point of Polish Holstein-Friesian Cows in Early Lactation

The objective of this study was to determine the relationship between milk β-hydroxybutyrate (BHB), acetone (ACE) as well as parity and lactation stage and milk freezing point (MFP) in Polish Holstein-Friesian cows in early lactation. Additionally, we studied the relationship between milk ketone bodies and daily milk yield (DMY), fat (MF) and protein (MP) content in milk. The data obtained from the Polish Federation of Cattle Breeders and Dairy Farmers, comprised 749,894 test day milk samples, collected between 6 and 60 days in milk (DIM) from 521,049 lactations of 514,066 cows. Milk BHB and ACE were determined using the Fourier transform infrared (FTIR) technology. Four classes of parities were created: first, second, third, and fourth to seventh and two classes of lactation stage: 5–21 and 22–60 DIM. BHB was grouped into five classes: ≤0.05, 0.06–0.10, 0.11–0.20, 0.21–0.50 and >0.50 mmol/L, and ACE was also classified into five classes: ≤0.05, 0.06–0.10, 0.11–0.15, 0.16–0.30 and >0.30 mmol/L. Data on MFP, DMY, and MF and MP content were analyzed using the MIXED procedure of SAS and a linear model in which effects of parity, lactation stage, BHB and ACE classes were included, together with interactions between lactation stage and BHB classes, parity and BHB classes, lactation stage and ACE classes, and parity and ACE classes. The differences among parity, lactation stages, BHB and ACE classes in MFP, DMY, MF and MP were highly significant. There was a clear tendency for decreasing of MFP with increasing of BHB. Such a trend did not occur in case of ACE. DMY and MP decreased and MF increased with increasing BHB or ACE. In conclusion, since MFP can be measured relatively easily and is well related to milk BHB content, it may be used in the prediction of diagnostic models of ketosis based on milk composition.